DESCRIPTION

These functions provide alternatives to using the gd_alter_entry(3)
function to modify a field of the indicated type in the dirfile
specified by dirfile.
In all of these calls, field_code indicates the the field to be
modified, which may be a regular field, or a metafield specified by its
full (slashed) field code, but should not contain a representation
suffix. The meaning and valid types of other arguments may be obtained
from the get_entry(3) and dirfile-format(5) manual pages. The gd_bit_t
type is a signed 16-bit integer type. The gd_shift_t type is a signed
64-bit integer type. The gd_spf_t type is an unsigned 16-bit integer
type.
The gd_alter_clincom() and gd_alter_cpolynom() functions are identical
to gd_alter_lincom() and gd_alter_polynom(), except they take complex
scalar parameters, instead of purely real values. This only matters
for the input of new parameters; if the scalar parameters are not
changed (by passing NULL instead of a list of scalars), the functions
can be used interchangeably, regardless of whether the altered field
has complex scalar parameters or not.
If the corresponding parameters are to be changed, the
gd_alter_lincom() and gd_alter_clincom() functions take pointers to
three arrays of length n_fields containing the input field names
(in_fields), the gain factors (m or cm), and the offset terms (b or
cb). Similarly, gd_alter_polynom() and gd_alter_cpolynom() take an
array of length poly_ord + 1 containing the polynomial co-efficients (a
or ca).
Some field parameters have special values which indicate no change
should be made to the parameter. Specifically, if any of the string
parameters or m, b, or a (cm, cb, or ca) are NULL, the old values will
be retained. Similarly, if spf, n_fields, numbits, cdividend, or
dividend is zero, or if bitnum is -1, or if data_type, or const_type
are equal to GD_NULL, these parameters will not be modified.
All field parameters introduced with this interface must contain
literal parameters. Field parameters which are scalar fields cannot be
introduced with these functions. To do that, use gd_alter_entry(3),
gd_alter_spec(3) or gd_malter_spec(3), as appropriate.
If rename_table is non-zero, the look-up table referenced by the
LINTERP field will be renamed to the path given by table. If recode is
non-zero, the binary file associated with the RAW field will be re-
encoded to reflect the new field parameters.
See NOTES below for information on using
gd_alter_clincom(), gd_alter_crecip(), and gd_alter_cpolynom() in the
C89 GetData API.

RETURNVALUE

On success, any of these functions returns zero. On error, -1 is
returned and the dirfile error is set to a non-zero error value.
Possible error values are:
GD_E_ACCMODE
The specified dirfile was opened read-only.
GD_E_ALLOC
The library was unable to allocate memory.
GD_E_BAD_CODE
The field specified by field_code was not found.
GD_E_BAD_DIRFILE
The supplied dirfile was invalid.
GD_E_BAD_ENTRY
One or more of the field parameters specified was invalid.
GD_E_BAD_FIELD_TYPE
The field specified by field_code was of the wrong type for the
function called.
GD_E_BAD_TYPE
The data_type or const_type argument was invalid.
GD_E_PROTECTED
The metadata of the fragment was protected from change. Or, a
request to translate the binary file associated with a RAW
field was attempted, but the data of the fragment was
protected.
GD_E_RAW_IO
An I/O error occurred while translating the binary file
associated with a modified RAW field, or an I/O error occurred
while attempting to rename a LINTERP table file.
GD_E_UNKNOWN_ENCODING
The encoding scheme of the indicated format specification
fragment is not known to the library. As a result, the library
was unable to translate the binary file be associated with a
modified RAW field.
GD_E_UNSUPPORTED
The encoding scheme of the indicated format specification
fragment does not support translating the binary file
associated with a modified RAW field.
The dirfile error may be retrieved by calling gd_error(3). A
descriptive error string for the last error encountered can be obtained
from a call to gd_error_string(3).

NOTES

The C89 GetData API provides different prototypes for
gd_alter_clincom(), gd_alter_cpolynom(), and gd_alter_crecip():
#defineGD_C89_API#include<getdata.h>intgd_alter_clincom(DIRFILE*dirfile,constchar*field_code,intn_fields,constchar**in_fields,constdouble*cm,constdouble*cb);intgd_alter_cpolynom(DIRFILE*dirfile,constchar*field_code,intpoly_ord,constchar*in_fields,constdouble*ca);intgd_alter_crecip(DIRFILE*dirfile,constchar*field_code,constchar*in_field,doublecdividend[2]);
In this case, the array pointers passed as cm, cb or ca should have
twice as many (purely real) elements, consisting of alternating real
and imaginary parts for the complex data. For example, ca[0] should be
the real part of the first co-efficient, ca[1] the imaginary part of
the first co-efficient, ca[2] the real part of the second co-efficient,
ca[3] the imaginary part of the second co-efficient, and so on.
Similarly, the cdividend parameter becomes a double precision array of
length two.